Similar to GDF15, FGF21 reduces the body weight through a non-adipose tissue effect; increases insulin sensitivity, adaptive thermogenesis, and uncoupling protein 1 (UCP1)-independent EE; and reverses hepatic steatosis (BonDurant et al., 2017; Chen et al., 2017; Desai et al., 2017; Hill et al., 2019; Ost et al., 2016; Pereira et al., 2017; Veniant et al., 2015; Xu et al., 2009). The gene discussed is INS; the disease is fatty liver disease.